This invention relates to the production of synchrotron radiation on a recirculation orbit of electron beam as accelerated by a radio-frequency (rf) accelerator, particularly to a method of reducing the rf power consumption by using an energy-recovery pre-accelerator.
The energy-recovery pre-accelerator is an rf accelerator by which an electron beam to be injected into the main accelerator is compressed and brought close to the speed of light so that it can be efficiently accelerated by the main accelerator. The present invention relates to a method of reducing the rf power that is supplied externally for beam acceleration by the pre-accelerator.
The rf accelerator is such equipment that a cavity is supplied with rf power to generate an rf electric field which is used to accelerate electron beams. Among the various types of rf accelerators proposed to date, an electron beam accelerator called an energy-recovery linac (ERL) is drawing increasing attention today. Being primarily intended for use as the next generation source of synchrotron radiation, ERL is most characterized by decelerating the once accelerated electron beam with the main accelerator on the recirculation orbit so as to recover the supplied rf power. As a result, the rf power input into the main accelerator can be drastically reduced despite the acceleration of the large-current electron beam.
As shown in FIG. 1, an electron beam generated from an electron source is accelerated and compressed by a conventional pre-accelerator and further accelerated by the main accelerator to produce synchrotron radiation on the recirculation orbit; thereafter, the electron beam is decelerated (has its energy recovered) in the main accelerator and discarded into a beam dump. Since energy recovery by deceleration is performed in the main accelerator, it can accelerate the large-current electron beam with a very small amount of power. This corresponds to an embodiment in which an electron beam from an electron source (injector) that has been brought to an energy of about 10 MeV and a length of about 3 ps with the conventional pre-accelerator is injected into the main accelerator on the recirculation orbit.
However, the conventional pre-accelerator which accelerates the electron beam does not perform energy recovery by deceleration, so it requires a very large amount of rf power (at least 100 kw) and hence an rf antenna (coupler) that withstands the large power input. This presents a substantial challenge in ERL construction. The rf antenna is needed to supply rf power into accelerating cavities in the rf accelerator.